1. Field of the Invention
The present invention relates to a device for measuring fluid flows through a porous body and, more particularly, through drilling cores of porous media originating from oil fields.
2. Discussion of the Background
In order to assess the performance of the various production mechanisms on a microscopic scale and to determine the quantitative parameters intended to supply the numerical production forecasting models, the current procedure is to run a fluid or displace several fluids in the drilling cores.
Devices for creating flows of fluid through drilling cores or samples have been known for a very long time. Reference may be made usefully to the article of G. L. Hassler, R. R. Rice and E. H. Leeman, entitled "Investigation on the recovery of oil from sandstone by gas-drive" (Trans. Aime. Vol. 118, page 116, 1936).
Less and less use is being made of the measuring devices comprising a plastic flow cell, usually used under "laboratory conditions", in favour of devices comprising a steel cell, the thickness of which makes it possible to withstand pressures of several hundreds of bars, at temperatures which may exceed 150.degree. C. In these latter devices, real samples or drilling cores are arranged in the cell and real fluids coming from the oil field are used. Production mechanisms may therefore be studied under real field conditions.
However, these devices, at the very least those which are used under "field conditions" because they make use of real fluids and drilling cores, make it possible only to assess the performance of the mechanisms studied on the basis of material balances between what is initially in the drilling core studied, what is injected therein and what is produced.
In fact, it is not possible to determine what is produced inside the drilling core, between the point of injection and the point of production In particular, nothing is known about local saturation distributions, about the form and deformation of displacement fronts which may be generated by heterogeneities or mobility ratios of unfavourable fluids or any other causes. This makes many interpretations risky and sometimes even impossible.
In order to monitor the flows within drilling cores, increasing use is being made, in measuring devices working under laboratory conditions with plastic cells, of gammagraphy, that it is to say measurement of the attenuation of an X or gamma ray by the material penetrated, attenuation which is a function of the density of the elements encountered.
As the metal cells of measuring devices under field conditions are not sufficiently transparent to X or gamma rays, it is proposed to replace the metal cell with a much less absorbent composite cell.
A cell of this type is described in GB-A-2,185,114. Said cell, intended for working with a scanner, was designed without piston tie rods, so as to be transparent at an angle of 360 degrees. It is produced by windings of filaments constructed of carbon fibres coated with resin, which winding is effected at two different angles so that the cell which is thus made of two layers, an inner and an outer layer, can withstand radial and axial pressures.
The device described in this patent has drawbacks even though it represents a substantial advance compared with prior measuring devices. In the first place the working life and efficiency of a layer constructed of a carbon fibre- and resin-based composite are lower than those of metal cells, because of the forces to which said layer is subjected, despite the fact that it may be very thick.
In the second place, mention should be made of the difficulties associated with leakproofness. An internal leakproof lining of elastomer fibre is used. It is known that the efficiency and working life of said lining are problematic, as well as installation thereof. Furthermore, said lining does not make it possible to have metal surfaces adjusted to the conventional standards in order to accept conventional O-ring seals. It is therefore necessary to install complex sealing joints between the cell body and the pistons, which, in addition to the disadvantages associated with doubtful reliability, prohibits any flexibility in the choice of the length of the rock sample to be studied.